73.

Discuss the characteristics of Group-13 elements in terms of metallic character and their tendency to exhibit inert pair effect. 

(i) Metallic character: The metallic nature i.e. electropositive character of elements increases from boron to aluminium (B<Al). It is due to a smaller size and higher ionisation potential of B than Al.

However, the metallic nature (electropositive character) decreases slowly from Gallium to Thallium (Al > Ga > In > Tl). This is due to the fact that the extra d-electrons in the atoms of these elements exert a very little shielding effect on outer electrons. Therefore, these electrons are more firmly held by the nucleus and hence there is a decrease in the metallic (or electropositive) character.

(ii) The tendency to exhibit the inert-pair effect. Inert pair effect means that the two s-electrons of the valence shell of heavier p-block elements form an inert pair and do not participate in bond formation. The tendency to exhibit the inert pair effect increases as we go towards the bottom of the group. For example, aluminium gives Al³⁺ in solution. Gallium, indium and thallium show +1 and +3 states. The stable state of thallium (Tl) is +1. This is due to the inert pair effect as 6s² electrons do not participate in bonding and only 6p¹ electron takes part in bonding.